I really want to know the consequences of helmet damage during EVA. Recently I watched a movie called "Mission to Mars" in which one of the astronauts sacrifices his life by taking his mask off. His face was badly affected.

$\begingroup$It's been several years since i watched that movie, but i remember being convinced at the time that it was really stupid that he sacrificed himself. The group as a whole have enough deltaV to rescue him if they go to him one at a time and expend all their fuel in deceleration, then the next one goes and does the same, etc... hope someone can chime in who maybe remembers the details more clearly$\endgroup$
– InnovineOct 19 '18 at 20:11

$\begingroup$@SteveLinton: Other question is about much smaller holes, not loss of a helmet or similar instant total depressurization. Answers don't work for this question.$\endgroup$
– Nathan TuggyNov 23 '18 at 10:44

5 Answers
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Don't ever take what's portrayed in a scifi movie as fact. You can use the fingers on one hand to count the number of scifi movies that go out of their way to be faithful to science. "Mission to Mars was not one of them. (Nor was Total Recall.)

Will you die if you take your helmet off in space? Of course. Your brain needs oxygen, as does the rest of your body. Without oxygen, you will go unconscious rather quickly. Then you'll die shortly later. You won't blow up. You won't instantly freeze. You might however get an ugly postmortem sunburn.

You do not explode and your blood does not boil because of the containing effect of your skin and circulatory system. You do not instantly freeze because, although the space environment is typically very cold, heat does not transfer away from a body quickly. Loss of consciousness occurs only after the body has depleted the supply of oxygen in the blood. If your skin is exposed to direct sunlight without any protection from its intense ultraviolet radiation, you can get a very bad sunburn.

$\begingroup$Your cited article is... unappreciative of the severity of decompression sickness. However, it won't happen during EVA due to the countermeasures (breathing a nitrogen-free atmosphere for multiple hours before EVA). The pressure drop when the mostly-flexible suit exits the pressurized spacecraft is more than the pressure left in the suit, and NASA is very aware that pressure drop would cause crippling, likely fatal DCS if nitrogen were still in the blood. So while loss of suit pressure is not so severe, depressurization of the spacecraft would kill even if oxygen masks were available.$\endgroup$
– Ben VoigtMar 19 '14 at 22:49

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$\begingroup$(I'm pretty sure that "blood boiling" is referring to decompression sickness, in which the partial pressure of nitrogen causes it to come out of solution and form bubbles)$\endgroup$
– Ben VoigtMar 19 '14 at 22:51

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$\begingroup$@BenVoigt - Given the portrayals in science fiction movies, I'm pretty sure "blood boiling" in that article refers to "blood boiling", not the bends.$\endgroup$
– David HammenMar 20 '14 at 10:34

$\begingroup$@E.P. -- Thanks for notifying me of the link rot. Instead of chasing a new link at nasa.gov, I used the wayback machine to link to its archived version of the page at the time that I wrote this answer.$\endgroup$
– David HammenJul 2 '16 at 22:59

Short story: your body will swell if not restricted by a suit, so the image does not look unlikely to me (Disclaimer: I'm basing this simply on what I've read about this topic so far, I don't know much about medicine.)

There was one fatal accident in space, Soyuz 11, which gives us an indication what happens. The three cosmonauts died when explosive bolts fired simultaneous instead of sequential while separating the orbital module and descent module, causing a pressure valve to open while they were still in space.

Relevant parts of the Wikipedia article:

On opening the hatch, they found all three men in their couches, motionless, with dark-blue patches on their faces and trails of blood from their noses and ears.

…

An extensive investigation was conducted to study all components and systems of Soyuz 11 that could have caused the accident, although doctors quickly concluded that the cosmonauts had died of asphyxiation.

…

The autopsies took place at Burdenko Military Hospital and found that the cause of death proper for the cosmonauts was hemorrhaging of the blood vessels in the brain, with lesser amounts of bleeding under their skin, in the inner ear, and in the nasal cavity, all of which occurred as exposure to a vacuum environment caused the oxygen and nitrogen in their bloodstreams to bubble and rupture vessels. Their blood was also found to contain heavy concentrations of lactic acid, a sign of extreme physiologic stress. Although they could have remained conscious for almost a minute after decompression began, less than 20 seconds would have passed before the effects of oxygen starvation made it impossible for them to function.

The pressurization for his right glove malfunctioned during the ascent and his right hand swelled to twice its normal size.

This incident is also mentioned in the "You Can Survive …" article:

From my previous experiences, I know that the hand will swell, lose most of its circulation, and cause extreme pain…. I decide to continue the ascent, without notifying ground control of my difficulty… Circulation has almost stopped in my unpressurized right hand, which feels stiff and painful… [Upon landing] Dick looks at the swollen hand with concern. Three hours later the swelling disappeared with no ill effect.

$\begingroup$"your body will swell if not restricted by a suit" that is wrong. The body will swell when exposed to not uniform pressure, that is was happened to Joseph Kittinger's hand. But under uniform pressure, no swelling by fluid shift takes place.$\endgroup$
– UweOct 22 '18 at 9:39

$\begingroup$@Uwe: Can you provide some sources for this? It seems the body doesn't swell due to fluid shifting but due to water vapor: This NASA study regarding the dogs says: The water vapor effect and gas expansion were of such magnitude that the animals became completely immobilized with the extremities, neck, and body in an extended position, similar in appearance to an inflated goat-skin bag. It talks about swelling in several places. I can't imagine a human body behaving differently here.$\endgroup$
– DarkDustOct 22 '18 at 10:28

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$\begingroup$@Uwe: Now you lost me. In your first comment: The body will swell when exposed to not uniform pressure, … and in your second comment: The NASA study [with swelling dogs] was done with dogs exposed to uniform low pressure. So why do you think a human body will not swell if exposed to uniform vacuum?$\endgroup$
– DarkDustOct 22 '18 at 11:12

$\begingroup$@OrganicMarble: I know about him but I don't know which conclusions we can draw from his accident regarding the swellings: AFAIK, by the time his colleagues were able to see him the chamber was already repressurized. So if he did swell a bit the swelling might already have been reversed. He did say that the last thing he remembers was feeling his saliva boiling on his tongue (but of course he/his blood did not boil). From the study: "the animals quickly and dramatically deflated to their normal appearance" so I'm note sure we can conclude from LeBlanc's accident that humans do not swell.$\endgroup$
– DarkDustOct 22 '18 at 15:27

If someone were teleported to mars without her spacesuit, she would first notice her tears, sweat, and mucous membranes boiling in the low pressure. Next, she would open her mouth to breathe, and her saliva would boil. In addition, with no oxygen in the Martian air, she would pass out from suffocation in 15 seconds. Bubbles of nitrogen would then form in her blood, causing her heart to stop and her to die.

If their helmet was breached, they would gasp for breath for about 10 seconds, while her exposed bodily fluids like saliva, tears, sweat, mucous and the liquid lubricating their lungs all boiled away, before she blacked out and their body swelled to twice its normal size. Their heart would try to keep pumping oxygenated blood to their brain to keep her alive, in vain. If they wer rescued to a pressurized, oxygenated spacecraft within 2 minutes they would most likely live, but if not they would die.

Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

$\begingroup$do you have a reference for the blood boiling? or references in general? What does this answer give that isn't included in the two that already exist?$\endgroup$
– JCRMOct 22 '18 at 9:28

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$\begingroup$While this answer is mostly correct as far as I know, it really needs some sources to back up these claims.$\endgroup$
– DarkDustOct 22 '18 at 10:32

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$\begingroup$The blood boiling directly contradicts the sources referenced in the other answers @DarkDust. Also, in my recollection, at two minutes, it's a "likely" to survive, not "would" survive.$\endgroup$
– JCRMOct 22 '18 at 10:42

$\begingroup$Plus 1 for being a new user and making the effort.$\endgroup$
– MuzeOct 22 '18 at 17:15

There was the Russian astronaut who had to empty his space suit to re-enter his ship on the very first space walk:

As they had with the first satellite and first man in space, the Soviets again stunned the world on March 18, 1965 with the first spacewalk (and the first EVA) performed by Alexey Leonov from the Voskhod 2 spacecraft, for 12 minutes outside the spacecraft. Leonov had no means to control his motion other than pulling on his 50.7-foot (15.5 m) tether. After the flight, he claimed this was easy, but his space suit ballooned from its internal pressure against the vacuum of space, stiffening so much that he could not activate the shutter on his chest-mounted camera

$\begingroup$As I recall it (and a better reference for that specific incident might be warranted), Leonov didn't actually "empty his space suit" (expose himself to a hard vacuum) but did have to reduce its pressure to below recommended minima in order to make it through the airlock of his spacecraft.$\endgroup$
– a CVnJan 30 '17 at 14:10

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$\begingroup$Leonov had to reduce the pressure of his suit from about 0.35 – 0.40 bar to just 0.20 – 0.27 bar. While this is very low, it's not vacuum.$\endgroup$
– DarkDustOct 22 '18 at 7:50